/*
 *  Copyright 1999-2004 The Apache Software Foundation
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 */

package org.apache.tomcat.util.collections;

import java.util.Vector;

/**
 * A simple FIFO queue class which causes the calling thread to wait
 * if the queue is empty and notifies threads that are waiting when it
 * is not empty.
 *
 * @author Anil V (akv@eng.sun.com)
 */
public class Queue {
    private Vector vector = new Vector();
    private boolean stopWaiting = false;
    private boolean waiting = false;

    /**
     * Put the object into the queue.
     *
     * @param    object        the object to be appended to the
     * queue.
     */
    public synchronized void put(Object object) {
        vector.addElement(object);
        notify();
    }

    /**
     * Break the pull(), allowing the calling thread to exit
     */
    public synchronized void stop() {
        stopWaiting = true;
        // just a hack to stop waiting
        if (waiting) notify();
    }

    /**
     * Pull the first object out of the queue. Wait if the queue is
     * empty.
     */
    public synchronized Object pull() {
        while (isEmpty()) {
            try {
                waiting = true;
                wait();
            } catch (InterruptedException ex) {
            }
            waiting = false;
            if (stopWaiting) return null;
        }
        return get();
    }

    /**
     * Get the first object out of the queue. Return null if the queue
     * is empty.
     */
    public synchronized Object get() {
        Object object = peek();
        if (object != null)
            vector.removeElementAt(0);
        return object;
    }

    /**
     * Peek to see if something is available.
     */
    public Object peek() {
        if (isEmpty())
            return null;
        return vector.elementAt(0);
    }

    /**
     * Is the queue empty?
     */
    public boolean isEmpty() {
        return vector.isEmpty();
    }

    /**
     * How many elements are there in this queue?
     */
    public int size() {
        return vector.size();
    }
}
